With the advancement in miniaturization of a semiconductor memory element, making a thinner charge accumulation film which constitutes a semiconductor memory element has been progressing.
A charge accumulation film acts as a charge accumulation layer. Moreover, the charge accumulation film acts as an entity of memory.
A metal-oxide-nitride-oxide-semiconductor, as a (MONOS)-type semiconductor memory device, also has been known.
The semiconductor memory element includes silicon nitride (SiN) as a charge accumulation film.
However, relative permittivity of SiN is approximately 9; therefore, a force of SiN to shield an accumulated charge is weak.
For this reason, the charge accumulation film cannot accumulate a sufficient amount of charge when the charge accumulation film is made thinner as described above.
Especially, when the neighboring memory elements share a continuous charge accumulation film, each of the memory elements cannot fully retain charges accumulated in the charge accumulation film.
Accordingly, there is a problem that the accumulated charges leak to adjacent memory elements.